An employee from the fast food joint's Booval location, a suburb of Brisbane, was filmed by a shocked customer drying a wet mop underneath the fry station's heat lamp ... shortly after she was done mopping the floor.

As you can see from the clip ... the employee makes no effort to hide her stomach-churning drying method -- she's doing it in plain view of customers.

She's taking her time ... holding up the damp, and likely extremely dirty, cleaning utensil just inches away from the hot lights and fries.

Debbie Barakat, the customer who filmed it all, told Yahoo! News Australia she was standing around waiting for her order when she heard a fellow staff member tell her, "I don't think you should be doing that as it could be a safety issue as it can catch on fire."

She said she also saw other employees working around the employee ... reaching over her mop-drying to grab fries to complete their orders.

A McDonald's Australia spokesperson said they take food safety extremely seriously and have addressed the restaurant directly.